It's nothing to do with isolation, more a timing thing so the optos won't help. Use
asm ("jmp 0");
To restart the chip, not quite the same as hard reset but usually good enough.
So I ask you why you need to initiate a reset as that is usually a case of not having proper program structure to begin with, as there is usually never a real need to perform a hardware reset that can't be solved by proper software?
Ooo, there's an echo in here 
some command will interact with the bluetooth modem but require a restart to take effect.
The Arduino is reset or the BT module? If the BT then none of the above applies. If the Arduino you must be storing information in EEPROM or other non-volatile memory or there is no point.
Rob